The law of conservation of energy, which states that the amount of energy in a system is constant. For questions about Earth's environment, see the climate-science tag instead.

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Greater momentum than initial?

The question is : Heavier object A, initially at rest, is struck by lighter object B. Is it possible for object A to have a larger final momentum than the initial momentum of object B? The ...
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2answers
59 views

Alternatives to the neutrino in the beta spectrum?

It is well known that the neutrino appeared to explain the power distribution in the beta decay spectrum. (see PSE) What other explanations candidates were available? It is stated that the ...
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3answers
80 views

How is energy converted when massless spring is attached to a rigid support

Say a massless spring of length l is attached to a rigid support. It is extended to length l + x. Now at this position, the ...
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2answers
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Finding the initial velocity of projectile [on hold]

What is the formula for calculating initial velocity of projectile using the conservation of energy given the mass, height, angle ?
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102 views

In a CMCS 2-body system, why does the speed of the particles after collision stay the same?

A particle $m_1$ is traveling with velocity $v$ toward a stationary particle $m_2$. The velocity of the center of mass is given as $v_c=\frac{m_1}{m_1+m_2}v$. Changing to a moving coordinate system, ...
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3answers
86 views

Violation of conservation of energy?

Imagine a perfectly spherical mirror with 100% reflection. Imagine a point source of light in the center. The point source keeps radiating light. Will the light undergo destructive interference ...
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1answer
55 views

Why does this not make infinite energy?

Here's an idea I had for infinite energy: Get into a spaceship, and fly to a star or other large body and get into orbit. Then just harvest your kinetic energy somehow and keep going indefinitely. My ...
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3answers
649 views

Where does the majority of the mass of the usual matter come from? [duplicate]

I apologize in advance to experts for the naivety of the question. It should be a duplicate but I didn't find any satifying question or answer about that. The proton is composed by two up quarks ...
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2answers
79 views

Why doesn't Beta Decay violate the laws of physics?

In Beta decay, a neutron decays into a proton, and "throws out" an electron at high speed. However, this, to me, suggests that the law of conservation of mass is not being kept here. Neutrons have a ...
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1answer
35 views

Why did the electric potential energy fall in this situation?

Suppose you have two capacitors configured as shown in the image below. One of them has charge $q$ and the other one is uncharged. Then, you close the switch, allowing charges to flow. After ...
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1answer
80 views

Isolation of a Physical System and Energy

I'm trying to grasp basic concepts of energy and i have a little doubt regarding conservation of energy. According to Feynman book and Wikipedia, the Law of Conservation of Energy states that ...
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2answers
166 views

Do virtual particles actually physically exist?

I have heard virtual particles pop in and out of existence all the time, most notable being the pairs that pop out beside black holes and while one gets pulled away. But wouldn't this actually violate ...
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3answers
356 views

Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
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1answer
135 views

Why don't virtual particles violate conservation of mass/energy?

If virtual particles sometimes add more mass/energy to a system then was inputed or comes out in the output, how do they not violate conservation of mass/energy.
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9answers
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How to explain independence of momentum and energy conservation in elementary terms?

I'm trying to explain to someone learning elementary physics (16 year old) that linear momentum and energy are conserved independently. I'm not a professional physicist and haven't tried to explain ...
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3answers
32 views

Velocity and transfer of energy for a body in free fall

I just need to check if my understanding of the transfer of gravitational potential energy to kinetic energy is correct. Is anything wrong below? Say if a body were suspended at a height h above the ...
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2answers
46 views

a question about work needed to move a charge towards another one [duplicate]

Consider two charges $q_1>0$ & $q_2>0$ separated by a distance $d_1$, and we want to move charge $q_2$ to a distance $d_2$ from $d_1$ where $d_1-d_2>0$. I need to calculate the work ...
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1answer
43 views

A captious work problem: same paths but same forces?

A man jumps onto a chair. A man climbs onto a chair by putting a leg first and then the other. In both cases, the work has been the same. TRUE or FALSE...? Spoiler!: The path is the same, so the ...
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3answers
666 views

The “binding energy” of bonded particles adds mass?

This is a follow-up my previous question. Several of the answers indicated that the mass of a particle (atom, proton, etc.) increase with the "binding energy" of it's component particles - the energy ...
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0answers
48 views

How to model the dissipation term

When a solid particle which is moving with $V_p$ collides with a droplet which is falling with $V_d$, based on what reported in literature, a liquid skirt will be formed as shown in figure below. One ...
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3answers
75 views

Ball on a slope with hollow

The experiment shown in the image suggests that ball B will reach the goal faster than ball A although the balls have identical properties and they start from the same height. The authors even ...
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3answers
241 views

Example of law of conservation of energy

Law of conservation of energy states that "Energy of the universe remains constant. Energy can neither be created nor be destroyed, but it can be transformed from one form to another". So I ...
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2answers
234 views

Question on particle decay process, conservation of energy

Why is $$\Sigma^0 \rightarrow \Lambda +\pi^0$$ not a possible process? Charge and baryon number both are conserved. There's no issue with strangeness that I can tell. The masses in $\frac{Mev}{c^2}$ ...
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3answers
64 views

Why does it hurt more to fall from 10 stories, than 1?

$F=ma$. Falling from any distance, mass stays the same, and acceleration due to gravity stays the same. So, why does it hurt more, the longer you fall?
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1answer
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Positions and corresponding terminology of “acoustics energy”?

From limited knowledge, decades ago, dating back to the nineteenth century: Ohm's law of specific acoustic energies was the first biological application of Fourier's theorem. Actually, it was ...
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3answers
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Conservation of momentum but not kinetic energy in inelastic collisions

In inelastic collisions, the kinetic energy of the system is not conserved but the momentum is. Kinetic energy is: $0.5 \times \text{mass} \times \text{velocity}^2$. Momentum is: ...
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1answer
364 views

Sufficient conditions for the energy to be not conserved?

I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics. Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. ...
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1answer
31 views

Question regarding the sail attached to a boat. [closed]

I came across a physics numerical in which the boat is travelling 45 degrees south-east. The direction of wind is towards north and the force that it exerts is constant force of 100 N on the sail. The ...
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3answers
61 views

Does (mass $\rightarrow$ pure energy) conversion need both matter $and$ antimatter?

A question in my revision guide: "Explain why the mass of a tree cannot be converted directly into energy." The answer explains that the tree contains particles but not their corresponding ...
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1answer
158 views

Why isn't jumping against a wall an elastic collision?

According to this calculator http://www.abecedarical.com/javascript/script_collision1d.html when low mass object hits high mass object it is reflected gaining opposite velocity almost the same as ...
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1answer
45 views

How can gravitational energy cancel out the rest energy of mass in the universe [duplicate]

I've heard that some physicists think that the net energy of the universe is zero. For this to happen, I would assume that the negative gravitational energy of a body ought to cancel out its rest ...
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1answer
248 views

How can a planet gravitationally capture objects?

I would expect that any asteroid or other object originating far away but passing near a planet would pick up speed and energy as it approaches, but unless it comes into contact with the atmosphere ...
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1answer
167 views

Conservation of energy when focusing black body radiation on another black body

This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics ...
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0answers
25 views

Spinning, decelerating coin on a table

A coin spun on a table will eventually end up flat on the table, ignoring the cases where it remains balanced and comes to rest on its edge (or falls off etc). Before the coin comes to rest on its ...
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2answers
32 views

Inelastic Collision and Energy

How is is possible for momentum to be conserved and for KE to not be conserved? Momentum is related to velocity and velocity is related to KE, therefore if KE was lost, how can the system have the ...
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3answers
645 views

Conservation of Angular Momentum, as related to a flywheel

Trying to work out some pesky flywheel dynamics for a project I'm working on, would love some for your assistance to better understand the underlying concepts. For a given flywheel (thin-walled ...
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3answers
443 views

Two dimensional elastic collisions with varying angle of incident

If in an elastic collision I know all initial values and that mass for each object remains constant throughout the collision (but different from one another) how can I determine their final velocity ...
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0answers
49 views

Is refraction of light a thermodynamic process?

Is refraction of light a thermodynamic process? Can it be explained by conservation of energy? If so, does temperature has an effect on refraction of light?
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2answers
392 views

If conservation of energy was wrong, how would we know about it?

Suppose you just started learning physics and you've been introduced to conservation of energy and kinetic energy. Apart from those concepts you know next to nothing. Then you observe an inelastic ...
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2answers
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What observations would be needed to falsify the law of conservation of energy? [duplicate]

I've been doing some thinking, and began to wonder: What observations have led us to the conclusion that ‘energy can neither be created nor destroyed’? Essentially, this means that the big bang ...
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2answers
4k views

Why can't I do this to get infinite energy?

I know that I cannot do this because of conservation of energy, so I am looking for an answer as to why this will not work. So by my understanding of Einstein's whole famous $E=mc^2$ thing it is ...
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1answer
168 views

The Uncertainty Principle and Energy Nonconservation

The uncertainty principle is listed in most textbooks and articles as $$ \Delta E \Delta t \geq \frac{\hbar}{2}.$$ This can be derived in many ways in many different settings, most of them involving ...
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4answers
219 views

If a bell is rung in a perfect vacuum and is suspended by opposing magnets will it ever stop ringing?

As far as I am aware a bell rung in a perfect vacuum would only lose energy and stop ringing due to friction between the bell and the hanging mechanism (due to the lack of air resistance). Therefore ...
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2answers
143 views

Does energy conservation not hold in fission and fusion processes?

I have read that during fission and fusion processes, there is some kind of equilibrium between the single nucleus and the disintegration products, so they are constantly being converted into each ...
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5answers
288 views

In an elastic collision, can we choose between cons. of energy and cons. of momentum?

Suppose we have two solid spheres with masses $m$ and $M$, respectively, and that $m$ is significantly less than $M$. The lighter sphere is placed directly on top of the heavier one, and the two are ...
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3answers
394 views

Energy Analysis of Niagara Falls in Linus Pauling's “General Chemistry”

I just started reading Linus Pauling's "General Chemistry" and the first example confuses me. He writes: Example 1-1. Niagara Falls (Horseshoe) is 160 feet high. How much warmer is the water at ...
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2answers
143 views

Dropping a weight onto a spring scale

Say I drop a 5kg weight from a height of 1 meters onto a spring scale like many people have in their bathrooms. On impact the scale will show a higher weight than 5kg. Question: Which quantities ...
2
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1answer
100 views

Weightless person in a cart on a rail [closed]

In a problem I'm trying to solve I'm having a conflict between my understanding and the proposed solution of the problem. In the problem, a cart of mass $m$ is put at rest in the start of a ...
2
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2answers
96 views

Where did energy come from?

So it is my understanding that before the big bang there was a very small point that held all of the matter in the universe. My question is what form did energy of the universe take on when it was in ...
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1answer
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Heat Equation with In-Depth Radiation Exact Solution [closed]

I am looking to solve the heat conduction equation in a semi-infinite solid with in-depth radiation on the domain $-\infty < x < 0$. The governing equation of this problem is: $$\rho c ...